Demographics and Characteristics
This study included 147 voluntary participants in the outpatient clinics of the Second Affiliated Hospital of Zhejiang University, School of Medicine, including 51 males (34.7%) and 96 females (65.3%) (Table 1). The mean age of all subjects was 37.69 ± 8.73 years. All participants were of Chinese ethnicity. Table 1 shows the basis information of all participants. Results of OSDI, CFS, Schimer I test and five FTBUT statistical types had no significant differences between the right and left eyes. The right eye of each participant was chosen for statistical analysis.
Comparison of Different FTBUT Values
Totally, five FTBUT diagnostic methodologies were analyzed after logarithmic transformation. Statistical differences are demonstrated in Figure 1. There were statistically significant differences between FTBUTmax and other four FTBUT values, but no significant differences were found among FTBUT1, FTBUT123, FTBUT12 and FTBUTmin.
ROC Curves of Five Different FTBUT Values
ROC curves and relevant analysis distinctly illustrated the capability and efficacy of each type of FTBUT value in diagnosing DED. The AUROC, cutoff point, sensitivity, specificity and Youden index of FTBUTmax, FTBUTmin, FTBUT1, FTBUT12 and FTBUT123 are displayed in Figure 2 and Table 2.
As indicated in Table 2, in the Shirmer I test, FTBUT123 had the largest AUROC of 0.810 (0.737 - 0.870), followed by FTBUTmax, whose AUROC was 0.792 (0.717 - 0.854). FTBUTmin had the smallest AUROC of 0.735 (0.656 - 0.804) (Figure 2A). FTBUT123 had a maximal Youden index of 0.497. When adopting the OSDI score as the diagnostic criteria of DED, FTBUTmax had the largest AUROC of 0.747 (0.669 - 0.815), followed by FTBUT123 [0.734 (0.636 - 0.780)], and FTBUTmin had the smallest AUROC of 0.695 (0.614 - 0.768) (Figure 2B). FTBUTmax had a maximal Youden index of 0.449. In the CFS test, FTBUT123 had the largest AUROC of 0.763 (0.690 - 0.832), followed by FTBUTmax [0.756 (0.673 - 0.818)], and FTBUTmin had the smallest AUROC of 0.700 (0.619 - 0.773) (Figure 2C). FTBUT123 had a maximal Youden index of 0.434.
Comparison of ROC Curves among Five Different FTBUT Values
The ROC curves of each two types of FTBUT values were compared by Medcalc and their p values are shown in Table 3. When dividing by Schirmer I test, ROC efficacy of FTBUTmax was significantly higher than that of FTBUT1 and FTBUTmin, but not different from that of FTBUT123 and FTBUT12. When dividing by OSDI, ROC efficacy of FTBUTmax was significantly higher than that of FTBUT123, FTBUT12, FTBUT1 and FTBUTmin. When dividing by CFS, ROC efficacy of FTBUTmax was significantly higher than that of FTBUT12, FTBUT1 and FTBUTmin, but not different from that of FTBUT123.
Correlations between FTBUT Values and Other Dry Eye Examinations
Pearson’s correlation analysis of logarithmic data and raw data was made. According to Table 4, FTBUTmax, FTBUTmin, FTBUT1, FTBUT12 and FTBUT123 were all closely related to Schirmer I test, the OSDI score and CFS, confirming that FTBUT examinations were reliable.
Distribution of FTBUTmax
The distributions of FTBUTmax among three FTBUT readings are shown in Table 5. The first, second and third FTBUT values were not significantly different (p = 0.133). The second FTBUT value turned out to be the largest and the first FTBUT value was the smallest. Intriguingly, among 147 FTBUTmax values, there were 62 second FTBUT values, 54 third FTBUT values and only 31 first FTBUT values.